The skin is the outer protective covering of the human body with an average total area close to 20 square feet, and composed of three layers namely the epidermis (outermost soft layer), the dermis (middle layer), and hypodermis (inner most layer made of strong connective tissues), with an average thickness of 1-4 mm. The skin is the first point of contact for any external load with the human body, and also the first barrier against any physical injury.
Skin simulants have been developed for burnt skin replacements and for medical training, such as for phlebotomical and surgical practice. Skin simulants are also useful in a variety of design and testing applications. For instance, skin simulants are employed during the development of ballistic munitions, especially in the context of non-lethal projectiles.
A successful skin simulant should accurately mimic the biomechanical properties of natural skin. Skin is a viscoelastic material and exhibits non-linear strain behavior. Furthermore, skin is not homogenous across either a single individual or a group of individuals. A single human will have skin tissues of differing stiffness, thickness and, depending on the specific location the skin occurs on the human body. As skin ages, collagen and other cellular components degrade, leading the skin to become less stiff.
Historically, intact skin obtained from human cadavers has been employed as a simulant, as well as skin samples from animals such as pigs, goats, and sheep. However, these materials present both ethical and practical challenges stemming from the harvesting and storage of biological tissues. As such, the use of synthetic skin simulants has been explored. U.S. Pat. No. 7,222,525 discloses skin/tissue simulant prepared from a gelatin block overlaid with an ether-cast polyurethane sheet. WO 2013/171444 describes a skin simulant prepared from a synthetic chamois, which can be prepared from various polymeric materials such as cotton, viscose, polyvinyl acetate, polyesters, and nylon-polyamide. These simulants, however, do not truly mimic the non-linear hyperelastic properties of true human skin.
Despite extensive research, a skin simulant having the realistic non-linear hyperelastic properties of the human skin has not yet been achieved. Realistic skin simulants would be of great use in a variety of biomechanical testing applications. For instance, a realistic simulant could be used to estimate the load response of cosmetic implants, or to further study the mechanics of skin injuries. A realistic skin simulant would be an invaluable aid for developing surgical techniques, especially for vaginal and other unique tissue types. In vaginal prolapse (POP), tissue stiffens progressively, making it difficult for surgeons to correctly suture and implants corrective devices. Faulty vaginal mesh surgeries have caused substantial pain and suffering in many women, and have resulted in malpractice lawsuits cumulatively totaling over 100 million dollars annually. To date, training for urogynoecological surgeries is limited due to the limited availability of vaginal tissue. In addition to ethical and safety concerns associated with sampling human vaginal tissue, it is known that vaginal tissue obtained from a cadaver is not the same as living tissue. As such, efforts to develop improved urogynocological techniques have been hampered.
The development of non-lethal and less-lethal munitions is an active area of research in the ballistics industry. A simulant with realistic mechanical properties of the human skin is essential in order to accurately predict the lethality of such munitions prior to their deployment in the field. The compositions and methods disclosed herein address these and other needs.